This is a pretty big subject with many schools of thoughts and it can get highly technical. In this post, I’ve tried to collate and condense key information that I’ve learnt over the years and write it up in short digestible chunks. The methods I will introduce here were collected from various books, people and through my own experience to fit my future purpose – a lazy man doing as little as possible to sustain a biologically diverse and active garden with plenty of kitchen waste. But there are common basics which remain the same whether you’re making it in a bucket in a high-rise apartment or creating a mound the size of a house with tractors. I will link information sources for further reading so that you can pick and collate your own perfect composting system if you get fired up.
Most of what we eat are either grown in soil or were raised eating things that grew in soil. In other words, plants, animals and humans rely completely on the continued capacity of soil to function as a vital living ecosystem. A teaspoon (1g) of healthy soil can contain 1 billion bacteria, meters of fungal filaments, thousands of protozoa and many nematodes. The more diverse and biologically active the soil, the more life it can sustain. And what supports these teaming organisms at the bottom of the food web is the the organic matter – decomposing and fully decomposed (humus) living things.
Topsoil is the top 13 to 25cm of soil where most of the organic matter and soil microorganisms are active but it takes between 200 to 400 years for nature to create one centimetre of top soil. That’s 2600 years for the 13cm in the shorter estimate, and 10,000 years for the 25cm with a longer estimate. Very rich soil with meters of top soil may have taken hundreds of thousands of years to accumulate.
Conventional agriculture depletes the topsoil through tilling and agro-chemicals, exposing the soil to erosion and destroying soil micro-organisms. If we degrade the soil quicker than it replenishes, we will eventually run out of topsoil responsible for sustaining life. The spongy quality that gives the ability to hold water through droughts vanishes. The soil dries out and becomes dust. The wind blows it away, or the rain washes it down the river into the ocean never to be seen again.
Half of topsoil on the planet has been lost in the last 150 years.https://www.worldwildlife.org/threats/soil-erosion-and-degradation
We are currently losing topsoil at 10 to 40 times the speed at which nature can replenish it. And scientists estimate that globally, we only have 60 years of topsoil left on which we can grow food. If we continue as we are now, there will be a 30% reduction in food production globally, while the demand for food increases by 50% in line with the rapid population expansion. Think about this: if we continue with current practices, within our lifetime the soil will be so degraded we will no longer be able to grow food.
Even moderately degraded soil will hold less than half of the water than healthy soil in the same location… a staggering paper was published recently indicating that nearly half of the sea level rise since 1960 is due to irrigation water flowing straight past the crops and washing out to sea.http://world.time.com/2012/12/14/what-if-the-worlds-soil-runs-out/
So there are some big reasons why we should compost to build soil fertility and maintain the integrity of our topsoil.
Composting is a process of breaking down organic waste such as our faeces, food and garden waste into rich fully decomposed matter called humus – full of nutrients, ready to be utilised by plants. If done well, in the right conditions, this process can take as little as two weeks.
One of the most important thing to note at the start is that composting is dependent on bacteria breaking down the waste. So setting up the right condition for these bacteria to thrive in is crucial. There are four distinct factors to consider: the air circulation, the ratio of carbon to nitrogen, the critical volume and the moisture content.
There are two different types of decomposition that can take place – anaerobic (without air) and aerobic (with air). Anaerobic bacteria becomes dominant in overly wet, compacted conditions and produces foul-smelling funk as it breaks down the material slowly- this is why many kitchen waste composts and other water logged composts have the intense putrid odour. The problem is often exasperated by the use of plastic compost bins that does not allow air to circulate.
There are multiple ways in which you can utilise this anaerobic process, including ways in which you can extract concentrated liquid fertiliser or to create biogas to cook such as in the video below. However, for the purpose of this post, I will be focusing on aerobic decomposition since it is much quicker and some quality compost for a gardens is the end product I’m after, not the gas.
Aerobic decomposition, as the name suggests, works best when it has plenty of air through it. One easy way to achieve this is to build a wire mesh composter like the one pictured below. It’s great for maintaining air flow, cheap to make and easy to release and rebuild for turning or for applying. It’s also possible to add aerating structure to the compost by adding slightly slower decomposing materials like wood chips or very thin twigs in layers.
If the compost heap has been created well, the pile will heat up as a byproduct of bacterial decomposition and begin to compress and shrink by up to a half in volume. The process will often slow down for several reasons but often it’s because there is less air circulation at the core as it reduces in size.
Turning the pile at this stage helps to mix the well decomposed compost at the core and not so decomposed outer layer. It also brings fresh oxygen in to the pile and kick starts the decomposition again. Some, with an army of volunteers, turns the pile every 2 days, and others use a thermometer to measure exactly when they should turn to keep it in the optimum temperature range. It’s true that by turning, you can get a usable compost in 2 to 3 weeks but I’m in no rush and I much prefer if I don’t have to lift heavy piles over and over, as I assume most of the readers here too.
What I’ve learnt recently is that if you’ve built up your pile well be prepared to wait a little longer, say two months, you won’t need to turn it. Read on till the end to find out.
Tip: I’ve been told by Thebeau to make the middle of the compost pile higher in a dome shape, since the central part will drop in volume the quickest and if you have a water permeable membrane covering the compost, you will get excessive rain pooling in the dip and drip into the core. This is especially important if you are going for the lazy method of not turning.
Without getting too technical (since the actual ideal carbon to nitrogen ratio, or C:N, is 25 to 30:1), the ideal is to mix about the same amount of high carbon materials that are normally quite BROWN with high nitrogen materials that tends to be GREEN. You can read more here and here if you want to get more mathematical.
50% High Carbon: shredded cardboard and newspapers, dried leaves, peanut shells, wood chips, straw, sawdust.
50% High Nitrogen: food waste, garden waste, animal manure, sea weed, cut grass.
The easiest way to achieve this at a home level is to make sure to cover the kitchen waste with equal amounts of wood chips or straw or brown leaves etc. It’s the same principle as compost toilets where you may put a scoop of saw dust on top of your deposit. The dried and usually airy high carbon material will absorb the excess liquid from your wet kitchen waste and balance out the humidity. The structure will allow the air to continue to circulate, activating the aerobic bacteria and suppress anaerobic activities, minimising the smell which often attracts flies and insects.
Although it’s hard to do at a household level, if you want to get some high quality compost relatively fast, you need to build a critical mass of 1m cube minimum. I think this is fairly easy to achieve if you live in the countryside, have a generously sized garden, grow a lot of your own veg and/or own a few animals. Or even in a city, I’ve met people who’ve collected kitchen waste from neighbours, asked for manure from local farms and got free delivery of spent malt from local breweries etc. I would recommend sourcing your raw material from organic sources since it’s best to avoid bringing in stuff that’s doused in glyphosate or its derivatives. Check out this incredible podcast for more information on why we should stay the fuck away from glyphosates.
This cubic meter volume can help you achieve the optimum core temperatures of between 55° C to 70°C which you should ideally keep for about 2 weeks if you’re needing to kill off pathogens – for example composting humanure or dog poo. At the lower end of 55°C, weed seeds are killed off so it’s worth spending a bit of time setting this up and make sure it maintains the higher temperatures. But it’s best not to get the pile over the 65°C mark since it will begin to kill even the thermophillic (high temperature loving) bacteria. It helps a lot if you own a compost thermometer like this one with a 50cm probe that’s deep enough to measure the centre of the pile. More on how to control the temperature here.
Tip: The best solution with minimum effort that I’ve come across was again at Thebeau’s farm where he created a meter cubed volume to start with and extended the compost pile longer into an elongated rectangle over time, adding daily build up of fresh green material and covering it with a layer of straw. I like this method for several reasons.
- It still achieves high temperatures with its volume.
- You can add small amounts in everyday.
- You can continue to add in raw materials in one end while extracting finished compost from the other end.
This is me building the first cubic meter with straw/horse manure mix. The straw has such structurally binding effect that if you carefully stack the pile on the edges, you can build the walls vertically or even slightly overhung. Note the green felt behind where the last compost pile is.
Notice the green felt, specifically designed for composting. The one he uses is an industrial sized 4m x 25m piece and from what I remember, he mentioned 800 euros so it’s a massive investment to begin with. But I’m sure you can get like a 4m x 5m version for much cheaper. There are several other reasons why this is an investment and not a wasteful expense.
- The felt will last for a decade or more. Divide the cost over 10 years and the amount of plastic you avoid adding to the landfill and it begins to feel like a fairly good deal.
- The fabric allows some moisture exchange, keeps the pile not too dry, not too wet. I believe Thebeau mentioned 10% or so water flow so 90% of the rain washes over the fabric. (The importance of this is explained in the last section).
- It allows air exchange, vital to aerobic decomposition unlike the black disposable plastic covers used in conventional agriculture.
- It’s foldable, portable and easy to set up – spread and cover your compost pile and you’re good to go. Fold out as you add more materials.
Maintaining the right moisture content in the pile is fairly easy if you’ve got the right condition, but it can be more challenging in drier or wetter climates. Most sources will tell you that you should aim for a level of saturation where a single drop of water drips out if you squeeze a handful really hard. I’ve never been too exact about this but I do try and hold a mental picture of that single drop every time I put my hands through the pile. Sprinkle some water, or preferably urine, to hydrate the pile if it feels dry. Don’t worry, the bacteria breaks down the pee so quick, there won’t be a trace of pee left next time you stick your hands in. Just make sure to ask first, if you’re peeing into someone else’s compost…
Tip: It’s a really good idea to cover your compost pile and protect it from rain. More than 40% of the nutrients can leach out of your compost with rain. Enormous quantities of nitrogen leaches with rain, far less but up to a quarter of potassium and the phosphorus remaining mostly intact. If you continue to apply this rain leached nitrogen deficient, phosphorus rich compost over a long time, you will inevitably create an imbalance in the soil fertility.
Other Really Useful Tips I Received From Experts
- Right at the start, add some recently finished good quality compost or top soil from a healthy forest to kick start the process.
- Avoid putting in weeds with seeds. If you do, keep the weeds in the center of the pile and make sure to create a minimum cubic meter pile to raise the core temperature to 55°C or more to kill the seeds.
- Chop up big pieces of waste and crush your egg shells so that they have more surface area to be worked on by the micro-organisms and speed up the process.
- Wood ash raises the alkalinity too high and kills off a lot of bacteria. If your soil is acidic, sprinkle wood ash on soil not on your compost.
- Any chunky branches thicker than your little finger will likely take too long to decompose and remain as branches. You can chip them if you have a chipper or intentionally use it in the pile to add aerating structure. Sieve it before use if you prefer not to have branches.
- Clay can hold onto a lot of nutrients and sprinkling one shovel of clay with about one wheel barrow of raw material can help to bind the available nutrients.
Meat and Dairy
Most composting experts advise not to put any meat in composts to avoid rodent infestation as well as to minimise the possibility of growing harmful bacteria. But why waste the dense nutrients of meat when there are several ways you can compost it.
- The hot composting can reach temperatures so hot that no mammals will go near it. The draw back is that you may need to keep the smelly decomposing meat in a bucket until you’re ready to create a pile.
- I’ve seen people use worm composting systems to decompose meat really quickly. I once seriously considered building a large scale wormery in a school I worked at to compost piles of leftover food but there was just too much to process (and summer holidays would kill the worms). Wormery or vermi-composting can be done in an apartment in tiny spaces so if you don’t have a garden you can still process your waste into compost for pot plants etc. Check out this family’s set up for minimum effort wormery.
- Here are some other methods. You can dry out the remaining bones, crush them and add them like bonemeals too.
There are many gardening books with chapters on composting but you may prefer a dedicated book such as this one here. Nicky Scott’s 40 years of composting know how condensed into a book.
Or perhaps you may have a large plot of land and want to know how else we could utilise the intense heat generated by the composting process. Check this book out to find out how to heat your water.